This invention relates generally to gas turbine engines, and more specifically to variable stator vane assemblies used with gas turbine engines.
At least some known gas turbine engines include a core engine having, in serial flow arrangement, a fan assembly and a high pressure compressor which compress airflow entering the engine, a combustor which burns a mixture of fuel and air, and low and high pressure turbines which each include a plurality of rotor blades that extract rotational energy from airflow exiting the combustor. At least some known high pressure compressors include a plurality of rows of circumferentially spaced rotor blades, wherein adjacent rows of rotor blades are separated by rows of variable stator vane (VSV) assemblies. More specifically, a plurality of variable stator vane assemblies are secured to the compressor casing wherein each VSV assembly includes an airfoil that extends between adjacent rotor blades. The orientation of the VSV airfoils relative to the compressor rotor blades is variable to control air flow through the compressor.
At least one known variable stator vane assembly includes a trunnion bushing that is partially positioned within a jacket. A portion of the airfoil extends through the trunnion bushing, and the VSV assembly is bolted to the compressor stator casing. In at least some known VSV assemblies, either polymeric or carbon bushings are used to provide a low coefficient of friction to facilitate minimizing friction and wear to the VSV assembly.
During operation exposure to the gas stream may cause erosion of the VSV bushings. Furthermore, gas stream leakage paths may develop within the vane assemblies as the bushing components erode. One such leakage path may develop between an outside diameter of the VSV airfoil and the inside diameter of the bushing. Continued operation with the gas stream leakage through the VSV bushings may adversely affect engine performance.
To facilitate preventing erosion of the polymeric bushings, at least some other known VSV assemblies use metallic bushings, wherein the mating components are fabricated from the same metallic material. However, metallic bushings have a higher coefficient of friction than the polymeric bushings, and the higher friction within the VSV assembly may also cause degradation of the VSV components. Alternatively, once the bushings have worn, worn bushings are replaced. However, the configuration of the VSV assembly may make replacing the bushings a time-consuming process that may include disassembling an extensive amount of the engine.
In one aspect a method for coupling a variable vane assembly for a gas turbine engine including a casing is provided. The variable vane assembly includes a bushing assembly and at least one variable vane that includes a platform and a vane stem. The method comprises coupling a first bushing to the engine casing in a press fit, coupling a second bushing to the variable vane, and coupling the variable vane to the engine casing such that at least a portion of the first bushing is between the engine casing and the second bushing, and such that at least a portion of the second bushing is between the first bushing and the vane stem.
In another aspect of the invention, a variable vane assembly for a gas turbine engine including a casing is provided. The variable vane assembly comprises a variable vane and a bushing assembly. The variable vane includes a platform and a vane stem extending outwardly from the platform. The bushing assembly includes an outer bushing and an inner bushing. The outer bushing is radially outward from the inner bushing such that at least a portion of the outer bushing is between the gas turbine engine casing and the inner bushing, and such that at least a portion of the inner bushing is between the outer bushing and the vane stem.
In a further aspect, a compressor for a gas turbine engine is provided. The compressor includes a rotor, a casing, and at least one row of variable vanes rotatably coupled to the casing through a plurality of bushing assemblies. The rotor includes a rotor shaft and a plurality of rows of rotor blades. The casing extends circumferentially around the plurality of rows of rotor blades, and the casing includes a plurality of openings extending therethrough. Each row of variable vanes extends between adjacent rows of the rotor blades. Each variable vane includes a platform and a vane stem extending outwardly from the platform. Each bushing assembly comprises an inner bushing and an outer bushing. Each outer bushing is radially outward from an inner bushing such that a portion of the outer bushing is between the casing and the inner bushing, and such that at least a portion of the inner bushing is between the outer bushing and each respective vane stem.